1. Field of the Invention
The present invention relates to a single-layer-electrode type charge coupled device (CCD) and a method for manufacturing the same.
2. Description of the Related Art
Recently, single-layer-electrode type CCDs have been developed by etching a single conductive layer with a fine photolithography and etching process to obtain electrodes whose spacing is about 0.2 to 0.3 .mu.m.
In the single-layer-electrode CCDs, since no overlapping of the electrodes is present, a capacitance between the electrodes can be small and no poor insulation is present between the electrodes. Further, since it is unnecessary to oxidize the electrodes to obtain insulation thereof, the electrodes can be made of metal or silicide in addition to polycrystalline silicon, to further reduce the resistances of the electrodes.
In a prior art method for manufacturing a CCD, a plurality of charge transfer electrodes are formed on a first insulating layer formed on a semiconductor substrate. Double conductive layers are formed on the first insulating layer. A second insulating layer is formed on the double conductive layers, and the second insulating layer is patterned by a photolithography and etching process. In addition, a sidewall insulating layer is formed on a sidewall of the patterned second insulating layer. The double conductive layers are etched by using the sidewall insulating layer as well as the second insulating layer as a mask, thus forming charge transfer electrodes (see: N. Tanaka et al., "Study of Single-Layer Metal-Electrode CCD Image Sensor", Proceedings of the Institude of Television Engineers of Japan, Vol. 50, No. 2, pp. 234-240, 1996). This will be explained later in detail.
In the prior art method, the spacing between the charge transfer electrodes, is decreased by providing the sidewall insulating layer on the sidewall of the second insulating layer.
In the prior art method, however, in order to reduce the spacing between the charge transfer electrodes it is impossible to increase the width of the sidewall insulating layer. In other words, the width of the sidewall insulating layer is generally dependent upon only the thickness of the second insulating layer.
On the other hand, when the thickness of the second insulating layer is increased, the step coverage characteristics of the overlying insulating layer are deteriorated, so that metal wiring layers are disconnected and the insulation breakdown characteristics between the charge transfer electrodes and the metal wiring layers are deteriorated.